ZyXEL Communications MES3500-24 User Manual

 Chapter 26 IP Source Guard

MES3500-24/24F User’s Guide

still available after a restart. To open this screen, click Advanced Application > IP Source Guard 
> DHCP Snooping > Configure.

DHCP Snooping Configure

The following table describes the labels in this screen.

DHCP Snooping Configure

Active

Select this to enable DHCP snooping on the Switch. You still have to enable DHCP 
snooping on specific VLAN and specify trusted ports.

Note: The Switch will drop all DHCP requests if you enable DHCP snooping and there are 

no trusted ports.

DHCP Vlan

Select a VLAN ID if you want the Switch to forward DHCP packets to DHCP servers on a 
specific VLAN.

Note: You have to enable DHCP snooping on the DHCP VLAN too.

You can enable Option82 in the DHCP Snooping VLAN Configure screen (

) to help the DHCP servers distinguish between DHCP requests from 

different VLAN.

Select Disable if you do not want the Switch to forward DHCP packets to a specific 
VLAN.

Database

If Timeout interval is greater than Write delay interval, it is possible that the next 
update is scheduled to occur before the current update has finished successfully or 
timed out. In this case, the Switch waits to start the next update until it completes the 
current one.

Agent URL

Enter the location of the DHCP snooping database. The location should be expressed 
like this: tftp://{domain name or IP address}/directory, if applicable/file 
name; for example, tftp://192.168.10.1/database.txt.

Timeout interval

Enter how long (10-65535 seconds) the Switch tries to complete a specific update in 
the DHCP snooping database before it gives up.

Write delay 

interval

Enter how long (10-65535 seconds) the Switch waits to update the DHCP snooping 
database the first time the current bindings change after an update. Once the next 
update is scheduled, additional changes in current bindings are automatically included 
in the next update.